Mesoporous silica is porous silica having mesopores with a diameter ranging from 2 nm to 50 nm, and is expected to be used, for example, as a carrier for functional materials or as an adsorbent. Known methods for producing the mesoporous silica include sol-gel methods using a surfactant micelle as a template, and methods forming a layered polysilicate as an intermediate.
Typical examples of silica-based particles currently mass-produced include glass flakes (scale-like pieces of glass). The glass flakes are used by being blended with matrix materials such as resin molded bodies and cosmetics. Flaky particles have a larger surface area than spherical particles. In addition, when a thin coating film is formed by a composition for application blended with flaky particles, the flaky particles are oriented in the coating film in such a manner that the principal surfaces of the flaky particles are parallel to the surface of the coating film, and a large proportion of the base material to which the coating film has been applied is coated with the distributed flaky particles. For these reasons, the flaky shape of particles is desirable in order to impart desired functions to matrix materials.
However, it has not been reported thus far that flaky mesoporous silica has been obtained which has mesopores suitable for treatments such as adsorption and decomposition of macromolecules such as proteins, and which is adapted to be blended with matrix materials.
The shape of mesoporous silica obtained by conventional sol-gel methods using a surfactant micelle as a template has been limited to a rod shape. In response, Patent Literature 1 discloses that sheet-shaped mesoporous silica can be obtained by using a surfactant that can form a ribbon phase or a nematic phase. However, the thickness of the sheet-shaped mesoporous silica obtained by this method is only less than 50 nm (claim 2 of Patent Literature 1). Such a thin sheet material is easily deformed, and is thus difficult to blend with matrix materials without any change in the shape.
In addition, in multi-layer mesoporous silica obtained by methods forming a layered polysilicate as an intermediate, pore channels extend along interlayer portions of the multi-layer structure, and therefore, surfaces that allow access to the mesopores are limited to only surfaces on which the interlayer portions are exposed. Accordingly, in the case of mesoporous silica having a structure composed of tabular crystals layered on each other, the mesopores cannot be accessed from the widest principal surface of the mesoporous silica. This makes it more likely that the exertion of functions via the mesopores is restricted. Also in view of mechanical strength, a multi-layer body has a problem in that part of the layers is likely to be separated by a stress applied when the multi-layer body is blended with a matrix material or when the matrix material blended with the multi-layer body is molded. The multi-layer structure having pore channels including mesopores and formed along the interlayer portions is not suitable as a basic structure of flaky mesoporous silica to be blended with matrix materials.